The present invention relates to stencil screen coating, usually for printing, and particularly to a submersion fluid transfer device to force fluid through the screen onto the underlying surface or substrate to be printed.
Screen stencilling is widely used for selectively depositing coating materials such as inks, adhesives, and other functional and/or decorative fluids through the pattern areas of a screen stencil onto underlying stock such as paper, polymers, cloth, wood, laminates, and the like, for making posters, decalcomania, graphic designs, and other purposes. The stock can be in various forms including sheet or web forms. Since screen stencilling is most commonly used for printing of inks, this invention will largely be explained with this usage for illustrative purposes.
Conventional squeegees are generally fabricated with a support plate and a resilient blade held in contact with a movable printing screen above print stock, such that, as relative motion is caused between the screen and squeegee, ink is forced through the screen by the squeegee to form a print on the stock. The ink or other fluid typically includes a fairly volatile carrier or solvent to be evaporated from the stock after the coating or printing step. Sometimes, however, the medium is temporarily placed in a fluid condition to allow printing thereof, after which it cools to a nonfluid state.
Specifically, in the conventional stencil printing process, a thin layer of ink is spread on the stencil screen, then the squeegee blade used to wipe the ink ahead of it on the screen while forcing a portion of the ink down through the mesh of the screen onto the stock. The screen is then recoated, and the process repeated. Ink must be repeatedly supplied to the screen between print strokes to provide sufficient ink for the operation. During the print stroke, the squeegee blade shifts the ink to an extreme end of the screen. A flow coater or the like then respreads the ink for another print stroke. This repeated shifting and respreading of the ink causes evaporation of the solvent or carrier of the ink, with consequent thickening and drying of the ink on the stencil screen. The amount of ink which can be applied to the screen at any one time is limited since, if a substantial amount of ink were applied, the squeegee would gush the ink over the edge of the frame at the end of the print stroke.
Thus, although a conventional squeegee works well in providing prints, the tasks of supplying adequate ink, and of maintaining uniform quality become a problem, particularly in a high speed screen press.